css Audio - Active file-generic CSS - Active Generic - Active HTML - Active JS - Active SVG - Active Text - Active file-generic Video - Active header Love html icon-new-collection icon-person icon-team numbered-list123 pop-out spinner split-screen star tv

Pen Settings

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

+ add another resource

You're using npm packages, so we've auto-selected Babel for you here, which we require to process imports and make it all work. If you need to use a different JavaScript preprocessor, remove the packages in the npm tab.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource

Use npm Packages

We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

⚠️ This feature can only be used by logged in users.

Code Indentation


Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <h1>🛠 Simple CSS+JS dynamic <code>max-height</code> accordions!</h1>

<h2>⚠️ The problem with <code>max-height</code> accordions</h2>
<p>I love the technique of using <code>max-height</code> to create accordions. <strong>Buuuuut</strong>, a big caveat is you can't transition between a <code>max-height</code> of <code>0</code> and <code>auto</code>. Leaving you to either:</p>
  <li>Use something like <code>max-height: 999em</code> to account for the tallest content length possible. This causes your opening and closing animations to be too quick.</li>
  <li>Use a smaller value for <code>max-height</code>, but what if your content is too large and it "cuts off" part of it?</li>

<h2>💪 transitionend to the rescue!</h2>
<p>You can add a <code>transitionend</code> eventListener to the accordion body (part that opens and closes) to dynamically calculate the <code>max-height</code> value! This event fires after a CSS transition completes. Meaning:</p>
  <li>When the accordion is closed the content is positioned absolute so we can hide the content, but still get the <code>scrollHeight</code> value</li>
  <li>When clicking a closed accordion we, store the <code>scrollHeight</code> in a variable and briefly set the <code>max-height</code> to <code>0</code>. We then immediately set the <code>max-height</code> to the value of the <code>scrollHeight</code> on the absolutely positioned element.</li>
  <li>Once the transition is complete we remove the <code>max-height</code> so the content isn't capped at this value. Otherwise, if you resize your browser you might have overflow issues.</li>
  <li>When a user closes the accordion we immediately capture the height again, set the <code>max-height</code> to this value briefly and finally change the <code>max-height</code> back to <code>0</code> to close the accordion seamlessly.</li>

<h2>🎉 Demo</h2>
<div class="Accordion" data-accordion>
  <div class="Accordion__title" data-title>
    <h3>Example Heading</h3>
  <div class="Accordion__content" data-content>
    <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Aperiam tempora voluptatum eligendi rem molestias numquam totam dignissimos animi ullam a culpa modi soluta, vero quisquam vel similique quibusdam neque nam?</p>
    <p>Ipsam dolorem ut similique ullam architecto eum corrupti dolor laboriosam neque error iure aliquam, inventore esse nemo, nisi laborum eaque, est officiis rem id. Doloremque velit excepturi eos tempore neque?</p>
    <p>Pariatur eius harum, quidem cumque corporis ipsa odio quo at, fugit atque inventore sit accusamus dolor unde? Porro ab nihil maxime sunt quasi? Asperiores animi, consectetur provident a aspernatur totam.</p>
    <p>Corrupti, voluptatem! Rem eveniet labore itaque velit amet vel sapiente qui harum quaerat aliquam veniam molestiae, corporis optio molestias magnam, nihil unde! Tempore voluptatem, quaerat sit neque repellat dignissimos earum?</p>

              .Accordion {
  border: 1px solid #ccc;
  border-radius: 5px;
  padding: 1rem;
  position: relative;

  &__title {
    cursor: pointer;
    user-select: none;

  &__title h3 {
    margin: 0;

  &__content {
    overflow: hidden;
    transition: .2s max-height;
    will-change: max-height;

  &.is-hidden &__content {
    position: absolute;
    opacity: 0;
    visibility: hidden;

 * Demo stuff
body {
  padding: 2rem;
  line-height: 1.5;

code {
  background: #4A484C;
  color: #fff;
  border-radius: 5px;
  padding: 0 8px;
              class Accordion {
  constructor($el) {
    this.$el = $el;
    this.$title = this.$el.querySelector('[data-title]');
    this.$content = this.$el.querySelector('[data-content]');
    this.isOpen = false;
    this.height = 0;


  events() {
    this.$title.addEventListener('click', this.handleClick.bind(this));
    this.$content.addEventListener('transitionend', this.handleTransition.bind(this));

  handleClick() {
    this.height = this.$content.scrollHeight;

    if (this.isOpen) {
    } else {

  close() {
    this.isOpen = false;
    this.$content.style.maxHeight = `${this.height}px`;

    setTimeout(() => {
      this.$content.style.maxHeight = `${0}px`;
    }, 1);

  open() {
    this.isOpen = true;
    this.$content.style.maxHeight = `${0}px`;

    setTimeout(() => {
      this.$content.style.maxHeight = `${this.height}px`;
    }, 1);

  handleTransition() {
    if (!this.isOpen) {

    this.$content.style.maxHeight = '';

 * Instantiate a new Accordion
new Accordion(document.querySelector('[data-accordion]'));
🕑 One or more of the npm packages you are using needs to be built. You're the first person to ever need it! We're building it right now and your preview will start updating again when it's ready.
Loading ..................